Start with the cut-out, not the screen
If the machine already exists, the panel has to fit a hole that is already punched. That makes the cut-out the first constraint, because changing an aperture means a new door, a new drawing and a new paint colour match.
The cut-out is part of the model code. In the SK series the letter after the size — A, B, F, G, H, M, Q or X — selects it, and several letters share an aperture at 7 inches (A/F/G and B/H/M/Q). That sharing is not cosmetic: it means a 7-inch panel can replace an older 7-inch panel without touching the sheet metal, and it means two models with different port counts can drop into the same hole.
Measure the aperture in both directions and compare against the cut-out column, not the bezel dimensions. The bezel dimensions tell you what can be seen; the cut-out tells you what will fit.
Decide the interfaces before the size
A panel with the wrong ports is more expensive than a larger panel with the right ones, because the fix is a converter or a second enclosure. Four questions settle it:
- Is there a controller already? If it is a Siemens, Mitsubishi, Omron or Delta, the panel needs the driver — the SKTOOL library carries more than 300 protocols, but the specific model should be checked, not assumed.
- Does the machine talk to anything else? An MES, a weighing terminal, a barcode scanner or a printer all need an interface. Ethernet with Modbus TCP covers most MES links; a USB host port covers a scanner or a memory stick.
- Will it ever be remote? If yes, buy the IoT model now. The module clips to the back of the panel, but retrofitting means a second shipment and a second installation visit.
- How many serial ports? A panel with one COM port and a controller that needs two is a problem nobody discovers until commissioning.
Resolution matters less than you expect, until it does
At 4.3 and 7 inches, 480×272 and 800×480 are usually enough for buttons, numeric entry and a bar graph. The resolution question becomes real in three places: trend curves with more than two pens, recipe tables with more than about eight columns, and screens read from more than a metre away.
For those, 1024×600 on a 7- or 10.2-inch panel is the practical threshold, and the 15.6-inch 1920×1080 model exists for full-line overviews. Reading distance is the variable to test: stand where the operator stands, at the size you are considering, and read a number.
The destination market decides half the specification
Export machines are certified where they land. Three items come up repeatedly:
- CE and FCC documentation. Declarations have to travel with the panel, not be requested afterwards. Ask for them with the quotation.
- Supply voltage. A DC 12–24 V panel is not the same as an AC-fed cabinet. Confirm what the machine provides before choosing a body.
- Language. The panel runtime supports 50 languages; the project file has to be built with the language switching in place, which is a design decision rather than a setting.
None of this is exotic, and all of it is cheaper to decide at the quotation than at the port.
A worked example
A labelling machine for a European customer. Existing door with a 192 × 138 mm aperture, a Mitsubishi FX-series controller, a Zebra printer and a requirement to log every label for traceability.
The aperture points at a 7-inch Q-cut-out panel. The controller needs an RS422 driver, which the SKTOOL library carries. The printer connects over the USB host port. Traceability means alarm and data logging, which the SK platform provides, plus enough memory for the record — 128 MB of flash is ample for label counts and alarm history.
That resolves to SK-070QS: 7-inch, 1024×600, Ethernet for the customer's MES later, two COM ports, USB host. The 10.2-inch SK-102QS would be the choice if the operator needed a bigger trend view, and it uses a different cut-out, so the decision has to be made before the door is drawn.